The WHO European Centre for Environment and Health has been closely following the research on green and blue spaces because of their importance in addressing human and ecosystem health in urban planning, especially in the context of climate change. Particular attention has been paid to the mental health effects of such spaces.  The EKLIPSE Expert Working Group on Biodiversity and Mental Health conducted two systematic reviews on the types and characteristics of green and blue spaces, in relation to a broad set of mental health aspects. The reviews demonstrated the overall positive relationship between green and blue spaces and mental health. This report summarizes the key findings of the systematic reviews, briefly looks at the relevant WHO tools and strategies, and reflects on future needs for research and action. The comparisons of the different green space types and characteristics produced mixed results, indicating that there is no one single space type or characteristic that is a “gold standard” that works best for everyone, everywhere and at any time.This work aims at supporting policy-makers responsible for planning, maintenance and protection of green and blue spaces, both at national and local levels.